Quasi-periodic pulsations and diagnostics of flaring plasma

Two approaches in the interpretation of quasi-periodic pulsations in solar and stellar flares are presented. The first presents flaring loops as resonators for magneto-hydrodynamic (MHD) oscillations. Leaky and non-leaky modes are discussed. The second approach is based on Alfvén’s idea of the flaring loop as an equivalent electric circuit. This approach naturally explains high-quality pulsations. It is shown that coronal seismology provides an efficient diagnostic tool for flare plasma on the Sun, red dwarfs, and in giant flares on neutron stars.